|Appears in||Call of Duty 4: Modern Warfare (Nintendo DS)|
O'Leary was the commanding officer of the Bravo Team that assaulted a cargo ship near the Caspian Sea containing a possible nuclear device. He and Bravo Nine infiltrated the main control room and disabled the navigational system. He then commanded Bravo Nine to destroy the ship's communication tower while he and a few others would go below deck, before Bravo Nine made his way below deck later on in the mission.
Once Bravo Nine destroys the tower, O'Leary ordered him to defuse two bombs the crew activated. Then he ordered Bravo Nine to go below deck, secure the nuclear warhead, secure the ship's manifest, and plant a charge in the engine room. Three Special Air Service operatives were sent to assist Bravo Nine, but an enemy helicopter retrieved the nuke and fled.
Although not actually present, O'Leary issued orders to the 11-man team sent to raid the bunker. The team's first task was to retrieve Ultranationalist troop deployment plans. Bravo Nine obtained the plans but narrowly avoided being killed by an explosion. Unable to contact him, O'Leary dispatched an operative to confirm Bravo's status. Bravo Nine proceeded with the mission, but the building began to collapse and O'Leary ordered all units to extract.
Colonel O'Leary was heard once again commanding an eight-man team, including Bravo Nine and L/Cpl Maras. Acting on information from the captured Ivan Petrovitch, the team was sent to recover the nuclear warhead carried by the cargo ship. Although at least two of the operatives may have been killed, Bravo Nine managed to reach the truck carrying the nuke. Just as the nuke's guards were defeated, the bomb was activated and O'Leary ordered him to disarm it as he was closest. Bravo Nine managed to jump onto the truck as it was leaving and disarmed it before it could detonate.
- He is named after Dan O'Leary, a co-founder of N-Space.
- Bravo Nine's initial failure to respond to O'Leary may have been meant to poke fun at Call of Duty protagonists' tendency to be silent.